ClO2 Measurement Influences - Known Behavior

Kuntze Instruments GmbH offers two methods to measure Chlorine dioxide. Which of these is better suited for your application/process depends on the chemical influences that are present in the water.

When unexpected ClO2 behaviors present themselves, it's important that the user understands both the Kuntze measurement and also the reference measurement. The reference measurement is commonly DPD, but more recently other handheld ClO2 reference methods have become available.  

1. Measuring parameter: ClO2

This measurement was developed specifically to measure ClO2 in the presence of Cl2. It responds to free chlorine only to approx. 10% of the ClO2 signal. In applications with concentrations of 0.20 mg/l of each ClO2 and Cl2 this would give a reading of 0.22mg/l ClO2.

This measurement also responds to some reducing agents by a smaller reading. The diminished signals can lead to deviations between the online measurement and DPD tests. In such cases, it might be advisable to use the parameter “chlorine”.

So far the following reducing agents have been found to interact while sensing ClO2:

- Chlorite

- Manganese(II), Iron(II)

- Hydrogen Peroxide

- Sodium Bisulfite

The reaction towards Chlorite can be used to monitor the efficiency of the ClO2 production process or the usability of prepared ClO2 solutions – if the production fails or the solution decays, Chlorite instead of ClO2 is dosed, with no disinfecting power but low limits due to its toxicity.

2. Measuring parameter: Cl2

This measurement selection responds to Chlorine and Chlorine dioxide in equal parts. A mixture of 0.2mg/L each of Cl2 and ClO2 will give a reading of 0.4mg/L.

On the other hand, this measurement does not respond to reducing agents. In applications with no Chlorine present, this parameter can be successfully used to measure ClO2 in the presence of Chlorite, Manganese(II) or bisulfite – as long as the chemical reaction between the substances leaves an excess of ClO2.